Delivery of fluids to and from a patient's body is often part of a medical treatment. A variety of mechanized fluid delivery system designs have been used. Generally speaking, these designs combine a valve mechanism to sequester the flow in one direction and a pump mechanism to deliver the flow in that direction. Most designs either use a push valve to push against a membrane and sequester the flow by occluding flow in one direction and then pump mechanism to displace a desired amount of fluid or use a rotary valve to sequester flow by a “scoop” while occlude flow in one direction and then using the pumping mechanism to deliver a desired amount of fluid. The desired amount of fluid is then provided to the patient.
In a typical push valve type system, fluid occlusion is achieved by advantageously employing the elastic property of a membrane. In practice, a push valve type system suffers from certain drawbacks. The fluid delivery mechanism of occlusion by pressing on a membrane forces the volume beneath the membrane to be delivered to both sides of the occlusion path. The fluid delivery mechanism's reliance on the elasticity property results in imprecise volumetric delivery of fluids. Furthermore, the volume dispensed through the system may be sensitive to the elevation of the pump, the fluid reservoir and the patient with respect to each other. The flow rate in a push valve type fluid delivery system may vary by as much as 20% based on the configuration of the reservoir and the patient.
In a typical rotary valve system, such as disclosed in the U.S. Pat. No. 4,605,396, a valve is rotated to alternately provide fluid communication through a groove between an inlet and a pump chamber or between the pump chamber and an outlet.
In practice, a rotary valve system has certain shortcomings. For example, priming such a system to expel air out of the fluid channels requires wasting some fluid by turning on the rotary valve and letting some fluid escape the delivery system to ensure air is removed from the system.